Liquid crystal displays (LCDs) are the dominant flat panel display technology in today's market. Conventional LCD systems include a network of optical components in front of a light source (e.g., fluorescent lamps, light emitting diodes (LEDs), etc.) commonly referred to as a backlight unit (BLU). Conventional backlight units include a light source coupled to a light guide through which the light travels eventually to a display panel. LED backlights employed in conventional systems include a set of optical films placed on top of an LED source, a slight distance away from the source. Among other things, the selection of a proper distance between the LED source and the associated optical films ensures that the light entering the display panel is properly optimized.
The quality of an LCD is often measured by a color gamut diagram. The color gamut refers to the total space of colors that may be represented by a display. Generally, the color gamut is shown by diagrams such as the International Commission on Illumination (CIE) 1931 XY color diagram. In this diagram, the gamut of available colors is represented by chromaticity on the x axis and brightness or luminance on the y axis. The gamut of all visible colors on a 2-D CIE plot is generally represented by a tongue shaped area in the center of the diagram.
Increasing the color gamut of a display device increases color quality and also leads to a higher perceived brightness. This effect is known as the Helmholtz-Kohlrauch (H-K) effect, which is defined as “Change in brightness of a perceived color produced by increasing the purity of a color stimulus while keeping its luminance constant within the range of photopic vision.” (See CIE Publication No. 17.4, International Lighting Vocabulary, Central Bureau of CIE, Vienna, 1988, sec. 845-02-34, p. 50.) This effect is dependent on ambient lighting conditions (i.e., the effect is enhanced under lower ambient lighting conditions and is diminished under higher ambient lighting conditions).
Two different LED light sources have been utilized in LCDs: (1) the combination of red, green and blue (RGB) LEDs and (2) white LEDs. Compared to the use of white LEDs, the use of RGB LEDs allows for a better color gamut but also adds significant complexity in implementation. The reduced complexity and, therefore reduced cost, of white LED backlights has caused these structures to be the implementation of choice in commercial LCD displays. Thus, some conventional displays have only a 70% color gamut (relative to the 1953 NTSC standard). In addition, some conventional LED sources require numerous color filters in the optical stack which increases power consumption.
LEDs commonly use phosphors to generate white light. The quality, color and directionality of light produced by LEDs are often poor. Optical components including quantum dots can be combined with an LED to produce light of certain wavelengths.
Accordingly, one object of the present invention is to increase performance of solid state lighting devices that utilize optical components including quantum dots.